1. Field of the Invention
This invention relates to a network system, more particularly, to a network system which has a plurality of lower switching hubs connected to network devices such as servers, storages and the like, and one or more upper switching hubs connected to each of the lower switching hubs, to relay normal frames transmitted and received between the lower switching hubs.
2. Description of the Related Art
In recent years, a network system having a broadband and band of which is extendable in the future has been required in accordance with an increase in information transmission quantity.
Accordingly, a network system using a plurality of switching hubs to realize a large-capacity virtual switching hub has been suggested by e.g. JP-A-2010-288168.
This network system has a plurality of lower switching hubs connected to network devices such as servers, storages and the like, and one or more upper switching hubs connected to each of the lower switching hubs, to relay normal frames transmitted and received between the lower switching hubs. This network system has a multipath configuration in which each lower switching hub is connected to all the upper switching hubs. Herein, the lower switching hub is referred to as port switch (PS) and the upper switching hub is referred to as fabric switch (FS).
Now, this network system is configured by using link aggregation. The Inventor has been developing a network system, which automatically configures a LAG (link aggregation group) by transmitting and receiving control frames between the port switches and the fabric switches. It should be noted that the link aggregation is a technique for virtually bundling a plurality of lines, to treat the bundled lines as if a single line, and is defined by IEEE802.3ad standard.
Here, automatic LAG configurations in the port switches and the fabric switches will be specifically explained.
The port switch is configured to transmit a control frame containing its own (source port switch) identifier, at predetermined time intervals, from all the ports connected to the fabric switches. Also, the fabric switch is configured to transmit a control frame containing its own (source fabric switch) identifier, the number of connected port switches, and connected port switch identifiers, at predetermined time intervals, from all the ports connected to the port switches.
In the port switch, a LAG is configured for all the ports connected to the fabric switches. The LAG configured at this point is referred to as a main link. Incidentally, in the port switch, the ports connectable to the fabric switches are predetermined, so that the main link is pre-configured for all of the ports connectable to the fabric switches.
Also, in the port switch, based on the contents of the control frames received from the fabric switches, a sub-link is configured for the ports connected to the same fabric switch. More specifically, in the port switch, a sub-link is configured for the ports received the control frames containing a maximum value of “the number of connected port switches” and the same “source fabric switch identifier”. Of the ports in the main link, the ports for which no sub-link is configured are disabled (prohibited) to transmit the normal frame, while the ports for which sub-links are configured are enabled (permitted) to transmit the normal frame.
On the other hand, in the fabric switch, a LAG is configured for the ports connected to the same port switch based on the contents, i.e. the source port switch identifier, of the control frames received from the port switches. Similarly to the port switch, the LAG configured at this point is referred to as sub-link. Incidentally, in the fabric switch, no LAG corresponding to the main link in the above port switch is configured.
With the use of the LAG, the ports for transmitting the normal frames are sorted in accordance with the contents such as source address, destination address of normal frames to be transmitted, thereby load is distributed, so that data can be transmitted at once. Therefore, the forwarding rate can be great, and the band can be extended. It should be noted that the normal frames are normal Ethernet (trademark) frames relayed with the port switch or the fabric switch.
In this network system, it is possible to flexibly extend the ports or extend the band by adding the port switches or the fabric switches appropriately. There is an advantage of reducing the cost for system introduction.
According to this network system, since a redundant configuration can be realized, there is another advantage that, even in the event of a failure of any path such as a transmission line between switches, communication can be continued through another path.